As disclosed in, for example, JP-A-2010-251837, a gateway apparatus for forwarding data frames between vehicle control units is known.
A vehicle is equipped with a lot of control units that control the vehicle. Various types of data are transmitted and received between the control units. An external diagnostic tool is connected to a vehicle network to perform a diagnostic communication with the control units. In the diagnostic communication, the diagnostic tool controls the control units and collects data from the control units.
Such data communication is performed using communication frames specified in communication standards such as controller area network (CAN) communications. For example, in the CAN communications, as shown in FIG. 7, a CAN identifier (ID) is assigned to each of nodes including a diagnostic tool, a gateway apparatus, an ECU1, and an ECU2. Specifically, the CAN ID is assigned for a receiving functional address Rx(F), a receiving physical address Rx(P), and a transmitting address Tx. The receiving functional address Rx(F) is set in a communication frame to transmit the communication frame to multiple nodes simultaneously. The receiving physical address Rx(P) is set in a communication frame to transmit the communication frame to a specific node. That is, the receiving functional address Rx(F) is a broadcast address, and the receiving physical address Rx(P) is a unicast address.
For example, when the diagnostic tool transmits data to the ECU1 and the ECU2 simultaneously, a CAN ID assigned as the receiving functional address Rx(F) is set in an address field of the communication frame. When the diagnostic tool transmits data to a specific ECU, a CAN ID assigned as the receiving physical address Rx(P) is set in the address field of the communication frame. When the ECU1 and the ECU2 transmits data to the diagnostic tool, a CAN ID assigned as the transmitting address is set in the address field of the communication frame.
As vehicles have become increasingly sophisticated, the number of ECUs mounted in vehicles has been increased. However, since the number of addresses assignable to each node is limited according to communication standards, the number of addresses assigned to each node may be not enough. For example, in CAN diagnostic communications, multiple diagnostic tools may be connected to a vehicle network. In such a case, as the number of diagnostic tools connected to the vehicle network increases by one, the number of usable addresses decreases by half. Therefore, it is difficult to assign enough number of addresses to each node.
For the above reasons, as shown in FIG. 7, when a communication frame is transmitted through a conventional gateway apparatus from the diagnostic tool to the ECU1 and the ECU2 simultaneously, the gateway apparatus prevents the ECU1 and the ECU2 from transmitting a response frame to the diagnostic tool.
In the light of communication quality, it is preferable that a unique transmitting functional address be assigned to each of the ECU1 and the ECU2 so that the ECU1 and the ECU2 can transmit the response frame to the diagnostic tool by setting the transmitting functional address in an address field of the response frame. However, in this case, collision may occur between the response frames transmitted by the ECU1 and the ECU2.